The substrates of magnetic recording media are typically glass or aluminum. Glass substrate supply constraints have resulted in aluminum becoming the preferred substrate. However, if the recording media processing temperature exceeds a threshold, an amorphous nickel phosphorous (NiP) layer employed with aluminum substrates is subject to crystallization, magnetization and surface roughening which can render a media unusable. Thus, recording media layer microstructure and magnetic properties are frequently limited by the thermal constraints imposed by the NiP layer.
For all types of substrates, magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and is now working toward densities of 800 Gbits/in2. Generally, PMR media may be partitioned into two primary functional regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional perpendicular magnetic recording disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
Higher areal densities are typically achieved with well-isolated smaller grains in the PMR layer 150. A higher magnetic anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise. US patent publication 2004/0185307 describes magnetic recording layers employing an ordered alloy such as CoPt and FePt having an L10 structure. While such an L10 ordered alloy in the PMR layer 150 can exhibit a high Ku that is beneficial for thermal stability and reduction of noise, the processing temperature which is conventionally required for such ordering to occur is relatively high and therefore relatively more expensive to manufacture than lower-temperature media. High ordering temperatures may also render L10-structured recording layers incompatible with a NiP layers, thereby limiting such media to glass substrates.
As such, lowering the ordering temperature of L10-structured recording layers in the PMR layer 150 advantageously reduces the expense of media manufacture as well as advances the art toward the goal of fabricating such media on aluminum substrates. Furthermore, by lowering the ordering temperature of the L10-structured recording layers, a higher Ku is achieved for a given recording layer formation temperature and therefore a media structure enabling a lower ordering temperature can also be utilized to improve Ku for any particular L10 alloy relative to the prior art.